疲劳累积损伤对发动机缸盖再制造的影响

通过对新、旧发动机缸盖取样进行疲劳试验,对比了其SN曲线,结果发现：应力幅较大时,新、旧缸盖材料的疲劳寿命相差明显;应力幅较小时,新、旧缸盖材料的疲劳寿命相差不大,表明旧发动机缸盖材料的损伤程度随着应力幅的增加而增大。因此当发动机经过再制造后,有可能因为累积损伤的原因存在安全隐患。     

不同装夹方式下的连杆疲劳寿命

目的分析大头间隙配合及大头小头均间隙配合这2种不同装夹方式,对连杆疲劳寿命的检测产生的不同的结果。方法采用MTS880±500 kN和MTS322±250 kN疲劳试验系统,采用不同的装夹方式模拟发动机工作状态,并通过"可靠性试验SAFL方法"进行数据处理。结果采用大头间隙配合装夹的连杆失效概率为5.2×10-5,大头小头均间隙配合装夹的连杆失效概率为0.87×10-5;并且2种装夹方式会影响连杆疲劳试验后的断裂位置。结论连杆疲劳试验中,采用大头小头均间隙配合装夹方式得到的连杆失效概率,较大头间隙配合装夹方式更小。进行疲劳试验需谨慎选择装夹方式。     

某车型发动机悬置螺栓连接失效原因分析

针对公司某车型发动机悬置支架与发动机支座连接螺栓在路试过程中发生疲劳断裂进行分析。本文从材料断口学、金相学等失效分析方法分析螺栓断裂原因;基于VDI2230螺栓连接计算系统对螺栓连接安全设计进行分析,从增大预紧力提高螺栓的疲劳性能进行分析。并对导致结构连接失效的原因提出优化设计措施,供汽车悬置支架连接设计相关人员参考。     

铝合金发动机缸盖的再制造技术研究

针对废旧汽车铝合金发动机缸盖的再制造需求,对发动机缸盖进行了失效分析,并研究了高速电弧喷涂Al-RE涂层的再制造工艺。实验结果显示,缸盖的失效主要表现为表面环形压痕和平面度超差,压痕区附近出现较多白色条状的Si相,硬度有所升高;高速电弧喷涂Al-RE涂层的组织致密,硬度略低于LM25TF铝合金基体,热压变形实验后涂层与铝合金基体结合良好,未出现裂纹和剥离。综合实验结果和典型零件的应用情况表明,高速电弧喷涂Al-RE涂层技术可实现铝合金缸盖的再制造。     

30CrMnSiA钢激光再制造件的性能

采用手工激光堆焊技术对预置一定尺寸缺陷的30CrMnSiA钢试样进行再制造,并对其进行了拉伸、冲击和旋转弯曲疲劳试验。结果表明:激光再制造试样的冲击性能和拉伸性能与原始状态材料试样的基本一致,但激光再制造试样的旋转弯曲疲劳寿命只有原始状态材料试样的约20%。断口分析发现疲劳裂纹源均产生在堆焊层,数量随着应力水平的增加而增多。     

曲轴材料48MnV钢及其具有3Cr13电弧喷涂涂层的疲劳行为

汽车发动机再制造中,采用电弧喷涂技术修复曲轴具有一定的潜在应用价值,本文对曲轴材料48MnV钢及其具有3Cr13电弧喷涂涂层的疲劳行为进行了研究。选用标准48MnV钢材料及其具有不同厚度涂层的试样进行拉伸和疲劳试验,计算了其疲劳极限并加以分析比较,同时对断口做了分析。发现基体材料为48MnV钢,具有3Cr13电弧喷涂层的试样在轴向载荷下的疲劳性能有相当程度的降低。涂层越厚,疲劳性能越差,疲劳极限越低。疲劳性能降低的主要原因是涂层的结合强度较小,以及喷砂时残留的铝氧化物引起疲劳裂纹萌生。     

发动机启动发电机弹性轴断裂分析

通过硬度检验、断口分析和金相检验等方法,确认断裂的发动机启动发电机弹性轴为扭转疲劳断裂失效,弹性轴锥体和衬套间配合松动导致的反复冲击是其断裂失效的关键因素,键槽设计的深度较大和加工质量粗糙进一步增大了转角处的应力水平,促进了裂纹萌生。     

HXD1机车牵引电机转轴组件断裂失效分析

HXD1型电力机车的牵引电机转轴和小齿轮轴采用圆锥过盈配合传动结构(下称转轴组件),使用中该组件出现了早期断裂失效.本文通过理化检测、断口和配合面宏/微观形貌观察等失效分析技术对失效组件进行了分析.结果表明,材料成分、组织和显微硬度正常,小齿轮轴和电机转轴的失效形式分别为高周疲劳断裂和微动疲劳断裂.造成组件失效的原因和过程是,小齿轮轴近齿端油槽-油孔交界线处有较大的结构应力集中,油槽底部周向加工刀痕造成附加应力集中,在应力集中和旋转弯曲疲劳载荷作用下油孔边两个应力集中点萌生了疲劳裂纹并扩展;随小齿轮轴裂纹的不断扩展转轴组件结构刚度减小,继而诱发了与小齿轮轴匹配的电机轴配合面的微动疲劳,电机轴疲劳裂纹萌生于微动区的边缘处;电机转轴先于小齿轮轴完全断裂.基于本文的分析结果提出了提高组件抗疲劳断裂的技术措施.     

航空发动机外部管路振动疲劳寿命估算方法研究综述

航空发动机外部管路长期在振动环境下工作，易产生振动疲劳损伤与失效。根据振动疲劳寿命估算方法，分析了时域和频域下航空发动机外部管路的振动疲劳寿命估算方法。给出了时域法和频域法对航空发动机外部管路寿命估算的适用特点，为航空发动机外部管路的振动疲劳寿命估算提供了理论依据。     

声发射技术在疲劳失效领域的研究进展

疲劳失效是一种具有突然性和灾难性的失效形式,因此对材料的疲劳失效进行监测显得尤为重要。与传统的疲劳裂纹检测方法相比声发射技术能够对材料的疲劳失效过程进行实时、在线监测,因此在疲劳失效监测领域得到了广泛的应用。对声发射技术进行了简要的介绍,总结了声发射技术在疲劳失效过程监测和疲劳寿命预测两方面的研究进展,指出了当前研究中存在的问题并对其下一步的发展进行了展望。     

Stepped‐isothermal fatigue analysis of engine piston

Stepped‐isothermal fatigue failure is the main failure mechanism of modern engine pistons under bench reliability test condition. This paper presents a methodology for stepped‐isothermal fatigue analysis of engine pistons, which consists of a fatigue criterion, evaluation of temperature and stress distribution by finite element analysis and the final life prediction. The major character of the methodology is the fatigue definition of engine pistons with respect to engine load change cycle and a damage‐based fatigue criterion accounting for the nonlinear creep–fatigue damage. Taking as an example, the fatigue life of an engine piston was predicted by the proposed analysis procedures. The analysis results showed that the most critical area was located in the throat edge. Moreover, the proposed methodology can give a relatively accurate and reasonable life prediction for an engine piston under the loading condition of bench reliability test, with a benefit of decreasing the needed component's reliability tests and design time.     

Microstructure and fatigue crack growth of EA4T steel in laser cladding remanufacturing

EA4T steel has been used widely in railway axles. Considering the failure behavior of railway axles and other solving methods, laser cladding remanufacturing was used for repairing the railway axles. The microstructure and fatigue fracture mechanism of EA4T steel in laser cladding remanufacturing were investigated by optical microscope (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The fatigue life and fatigue crack growth were measured by three-point bending experiments. The microstructure of cladding layers was composed of columnar crystal and fine dendrites, and the main phases of cladding layers were γ and Fe₂B shown by XRD results, which lead to the highest micro-hardness value in the cladding layer. The da/dN-ΔK curves and fracture morphologies indicate that the cladding layers could delay the fatigue crack initiation and improve the fatigue life of EA4T steel.     

A high-cycle fatigue apparatus at 20 kHz for low-cycle fatigue/high-cycle fatigue interaction testing

High-cycle fatigue (HCF) failures in aircraft engines are attributed to material damage states, created during processing or by in-service loading and environmental conditions, and then propagated to failure by HCF loading. The loading configuration experienced by aircraft engine turbine blades consists of an axial load caused by the centrifugal acceleration during rotation combined with the tensile and compressive loads caused by the natural vibrations of the blades themselves. To simulate these loading conditions a new testing apparatus was developed that is capable of providing interactive low-cycle fatigue/high-cycle fatigue (LCF/HCF) loading, in ratios (of magnitude and frequency) that give a realistic simulation of the actual flight loads experienced by engine components. This testing apparatus is based on a HCF cell operating at 20  kHz. The cell can also be integrated to a servo-hydraulic load frame, which provides a second fatigue cycle. The objective of this study was to demonstrate the capabilities of the new HCF apparatus via thermographic measurements and by performing LCF/HCF interaction tests.     

Analysis of a diesel generator crankshaft failure

This paper analyses a catastrophic crankshaft failure of a four-stroke 18 V diesel engine of a power plant for electrical generation when running at a nominal speed of 1500 rpm. The rated power of the engine was 1.5 MW, and before failure it had accumulated 20,000 h in service operating mainly at full load. The fracture occurred in the web between the 2nd journal and the 2nd crankpin. The mechanical properties of the crankshaft including tensile properties and surface hardness (HV₁) were evaluated. Fractographic studies show that fatigue is the dominant mechanism of crankshaft failure, where the beach marks can be clearly identified. A thin and very hard zone was discovered in the template surface close to the fracture initiation point, which suggests that this was the origin of the fatigue fracture. A finite element model of the crankshaft has predicted that the most heavily loaded areas match the fractured zone.     

装备再制造工程与失效分析

装备再制造工程是以实现废旧装备性能跨越式提升为目的的系统工程，基于循环经济4R准则即减量化（Reduce）、再利用（Reuse）、再制造（Remanufacturing）和再循环（Recycle）的装备再制造工程是建设节约型社会的重要手段，具有重要的社会经济意义。装备再制造工程与失效分析关系密切，失效分析是装备再制造工程的基础和前提，装备再制造工程是失效分析的结果与发展。结合失效分析和再制造工程实例，阐述了失效分析和再制造工程的相互关系及其在工程中的联合作用。     

Fatigue Fracture of a Compressor Disc of an Aeroengine

There was an accident to a single engine aircraft. From the eye and ear witness accounts, it was established that the accident occurred because of engine failure. After preliminary examination of the wreckage of the crashed engine, a few suspected components were identified for detailed laboratory investigation. The objective was to establish the primary failure in the engine. While majority of the engine components submitted for laboratory analysis showed secondary damages due to either crash impact forces or post-accident fire, the fracture pattern in one of the compressor disks was different from other components of the engine. Fractographic study revealed that the failure of the disk was by fatigue mechanism. Subsequent investigation showed that the fatigue fracture of the compressor disk was the first in the chain of events that led to the engine failure. This finding was further substantiated through fracture mechanics calculations.     

Managing Coordination Complexity in the Remanufacturing of Aircraft Engines

The complexity of communication and coordination stemming from teams responsible for adjusting interdependent parameters of components is a fundamental feature in the aircraft engine remanufacturing engineering project. To manage coordination complexity, the features of the remanufacturing process of aircraft engine are analyzed and a systematic method is presented to measure and optimize the dependency between coupled components. Furthermore, quantitative models are built based on Design Structure Matrix (DSM) models to measure dependency strengths related to the parameter features of the components. Also, a two-stage DSM clustering criteria is used to reduce the complexity of an organization. An industrial example is provided to illustrate the proposed models. The results showed that the proposed approach can reduce total coordination complexity.     

Fatigue failure of a stainless steel wires used in a hydraulic pressure line

A Boeing B767-300 experienced a right engine fire during taking off. The inspection of the right engine’s fuel system revealed a failure in the turbine case cooling (TCC) air valve actuator hydraulic pressure line, a flexible component made of AISI 304 stainless steel wire braid. The failure occurred in an area of broken wires in the braid that was located at the edges of a kink in the line associated with a bending. The examination of the broken ends of the wires by means of the use of field emission scanning electron microscope (FESEM) revealed fractures features that were indicative of fatigue failure, with very fine fatigue striation spacing, thus indicating at least 1000 cycles to failure. The energy dispersive X-ray (EDX) analysis did not reveal any defects acting as initiation source. Rather, the failure resulted from the permanent deformation of the line, thus developing a stress concentration at the kink. Following these results, new safety recommendations were suggested and subsequently adopted.